ABSTRACT Among men who have sex with men (MSM) testing for HIV in the United States (US), approximately 60% of all incident HIV infections occur in men reporting the highest quartile of risk behaviors. Young MSM (i.e. those ?24 years of age; hereafter ?YMSM?) are disproportionately represented in the highest risk quartile, have rates of HIV incidence twice as high as older MSM, and are less likely to take preexposure prophylaxis (PrEP) for the prevention of HIV. As a high-impact prevention strategy, the CDC recommends YMSM test for HIV once every 3-6 months. Alarmingly, we recently documented risk behaviors increased in direct proportion to the number of repeat negative HIV tests among MSM, despite routine risk-reduction counseling. The dynamics behind increasing risk behaviors in repeat testers are poorly understood. Increased risk behavior may lead to more frequent (and appropriate) HIV testing or perhaps more frequent HIV testing gives rise to increased risk behavior (i.e., negative test results may be interpreted as positive reinforcement that ongoing risk behaviors are not sufficiently risky to result in HIV infection). In either case, current public health efforts to increase HIV- testing in the highest risk quartile are likely to capture more YMSM, and studies are needed to delineate the drivers of ongoing or increased risk behavior in YMSM after testing to develop more effective interventions to promote HIV prevention. Given the push to increase repeat HIV testing among YMSM in the US, gaining a better understanding of if and how repeat testing influences risk perception and risk behavior is critical. We propose a novel study to assess perceptions of receiving negative HIV test results and how they are associated with HIV risk and prevention behaviors over time in YMSM. To explore the attributions and ?meaning? YMSM make of negative HIV test results over time, we will perform cross-sectional in-depth qualitative interviews (n=20; phase 1) in PrEP-nave HIV repeat testers receiving negative HIV test results, followed by quantitative assessment and monitoring of patterns of self-reported risk behaviors and perceived risk over time (n=115; phase 2) in YMSM. Purposive sampling for the qualitative interviews will stratify recruitment by self-reported risk behavior at their two most recent testing encounters. Qualitative findings will be incorporated into a validated questionnaire that quantitatively measures psychological reactions to the receipt of negative HIV test results. In phase 2 of the study, the adapted questionnaire will then be delivered together with monthly microsurveys to assess development of self-reported risk and prevention behaviors, as well as perceptions of HIV-exposure risk before receiving the negative HIV test result and over 12-months after the testing encounter. The proposed study will inform strategies to modify or develop prevention interventions delivered during repeat HIV testing and counseling sessions.